libsass: fix runtime version when using git shallow tarball

libsass: fix runtime version when using git shallow tarball

Add tag to SRC_URI to fix runtime version when using git shallow
tarball.

Before the fix:
$ sassc --version
sassc: 66f0
libsass: 7037
sass2scss: 1.1.1
sass: 3.5

After the fix:
$ sassc --version
sassc: 3.6.2
libsass: 3.6.6
sass2scss: 1.1.1
sass: 3.5

Signed-off-by: Yi Zhao <yi.zhao@windriver.com>
Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>